php Trait基类use trait,本类不use

一 回顾trait使用

https://blog.csdn.net/bushuwei/article/details/103514174
发现之前本人说明很模糊，自己居然不知道为什么
其实这里的$c,就是class B
再次回顾逻辑

二 分析

• self和static区别说的没毛病
• Trait基类use trait,本类不use。那么如果用的new self，则你new 出来的就是 use trait者。如果new static，则因为有继承关系， 它会判断类是否存在(父子会被认为都是同一个static，则不再new)，那么，谁先调用instance，那么new出来的就是谁。‘Trait基类use trait,本类不use’->直接‘其实这里的$c,就是class B’是错的。之所以有这个‘幻觉’，是因为单例模式，且static

三 上代码

1. self+单例

   trait A{
       private static $instance;
       static function getInstance()
       {
           if(!isset(self::$instance)){
               self::$instance = new self();
           }
           return self::$instance;
       }
   }
   
   class B{
       use A;
       function a()
       {
           var_dump('call at B');
       }
   }
    
   class C extends B{
       function a()
       {
           var_dump('call at c');
           parent::a();
       }
   }
    
   class D extends B{
       use A;
       function a()
       {
           var_dump('call at D');
           parent::a(); 
       }
   }
   $b = B::getInstance();
   $c = C::getInstance();
   $d = D::getInstance();
    
   $c->a();
   echo "<br/>";
   $d->a();
   echo "<br/>";
   

   　　

   string(9) "call at B"
   string(9) "call at D" string(9) "call at B" 

   注视掉

   // $b = B::getInstance();
   结果不变

2. static+单例

   trait A{
       private static $instance;
       static function getInstance()
       {
           if(!isset(self::$instance)){
               self::$instance = new static();
           }
           return self::$instance;
       }
   }
   
   class B{
       use A;
       function a()
       {
           var_dump('call at B');
       }
   }
    
   class C extends B{
       function a()
       {
           var_dump('call at c');
           parent::a();
       }
   }
    
   class D extends B{
       use A;
       function a()
       {
           var_dump('call at D');
           parent::a(); 
       }
   }
   $b = B::getInstance();
   $c = C::getInstance();
   $d = D::getInstance();
    
   $c->a();
   echo "<br/>";
   $d->a();
   echo "<br/>";
   

   string(9) "call at B"
   string(9) "call at D" string(9) "call at B" 
   

   　

   注视掉

   // $b = B::getInstance();

   string(9) "call at c" string(9) "call at B"
   string(9) "call at D" string(9) "call at B" 

    

3. 　self+非单例

   　　

   trait A{
       private static $instance;
       static function getInstance()
       {
           self::$instance = new self();
           return self::$instance;
       }
   }
   
   class B{
       use A;
       function a()
       {
           var_dump('call at B');
       }
   }
    
   class C extends B{
       function a()
       {
           var_dump('call at c');
           parent::a();
       }
   }
    
   class D extends B{
       use A;
       function a()
       {
           var_dump('call at D');
           parent::a(); 
       }
   }
   $b = B::getInstance();
   $c = C::getInstance();
   $d = D::getInstance();
    
   $c->a();
   echo "<br/>";
   $d->a();
   echo "<br/>";
   

   　　

   string(9) "call at B"
   string(9) "call at D" string(9) "call at B" 
   

   　　注释掉

   // $b = B::getInstance();

   结果不变

4.  static+非单例

   trait A{
       private static $instance;
       static function getInstance()
       {
           // if(!isset(self::$instance)){
           //     self::$instance = new static();
           // }
           // return self::$instance;
           self::$instance = new static();
           return self::$instance;
       }
   }
   
   class B{
       use A;
       function a()
       {
           var_dump('call at B');
       }
   }
    
   class C extends B{
       function a()
       {
           var_dump('call at c');
           parent::a();
       }
   }
    
   class D extends B{
       use A;
       function a()
       {
           var_dump('call at D');
           parent::a(); 
       }
   }
   $b = B::getInstance();
   $c = C::getInstance();
   $d = D::getInstance();
    
   $c->a();
   echo "<br/>";
   $d->a();
   echo "<br/>";
   

   　　

   string(9) "call at c" string(9) "call at B"
   string(9) "call at D" string(9) "call at B" 
   

   　　注释掉
   $b = B::getInstance();
   结果不变

四 结论

• self的话，就是谁use的，就是谁
• static的话，谁调用的就是谁
• 但是static会出现‘谁use就是谁’的幻觉，那是因为单例模式，前面创建了相同类型的单例。

原文链接：https://www.cnblogs.com/bushuwei/p/17277267.html